Unfortunately, 5.1 Surround Sound is currently not available. There is a feature request for higher audio quality in our FR board. Feel free to check it out and vote for this idea here.
Here are some details regarding audio quality on Pandora:
For listeners accessing Pandora from a computer, Ad-supported Pandora is 64kbps AAC+, while Pandora Plus and Pandora Premium subscribers have the option of 192kbps.
On Android and iOS devices, ad-supported listeners and Pandora Plus subscribers get anywhere from 24kbps to 64kbps in mono or stereo, depending on the phone, carrier, connection type and - in some cases - the user's settings. Only Pandora Premium subscribers can receive 192kbps on their iOS and Android devices.
Most home-listening devices get 128kbps - whether the account is free or paid.
Thanks for posting!